A remediation agent for repairing DNAPL pollution based on chemical oxidation and a preparation method thereof

Abstract

The application discloses a remediation agent for repairing DNAPL pollution based on chemical oxidation and a preparation method thereof. The remediation agent comprises 32.5-49.5 wt% of an oxidant and 50.5-67.5 wt% of a composite leaching agent. The composite leaching agent is composed of 12.5-24.5 wt% of sodium dodecyl sulfate, 21.5-32.9 wt% of a plant polyphenol polyoxyethylene ether, 6-18 wt% of polyethylene glycol and 24.6-60 wt% of deionized water. DNAPL pollutants existing in soil are leached out by the composite leaching agent, and the leached DNAPL pollutants are treated by oxidation. When DNAPL pollutants exist in areas where oxidants cannot reach, such as fractured layers or clay layers, or when soil or stones prevent the oxidant from diffusing quickly, completely and uniformly, the repair period of in-situ chemical oxidation technology is greatly prolonged.

Description

Technical Field

[0001] This invention relates to the field of environmental remediation technology, specifically to a remediation agent and its preparation method based on chemical oxidation for remediating DNAPL contamination. Background Technology

[0002] DNAPL is a typical type of organic pollutant in groundwater, primarily composed of organic substances denser than water and poorly soluble in it. As an important industrial raw material, DNAPL is widely used in agriculture, fuel, and pharmaceuticals. Accidents and improper handling during production, transportation, storage, and use can cause DNAPL to enter the soil. Under gravity, it continuously infiltrates into extremely small pores or penetrates clay layers, accumulating to form DNAPL contamination pools. Once in the groundwater environment, DNAPL releases its pollutants slowly and continuously due to the very slow mass transfer process from the pure phase to the dissolved phase. Furthermore, because of its low biodegradability, DNAPL's natural decay in the groundwater environment is slow; therefore, the remediation of DNAPL pollution sources is often referred to as "perpetual remediation."

[0003] However, in current DNAPL remediation, the remediation cycle of in-situ chemical oxidation technology is greatly prolonged when DNAPL contaminants are located in areas where oxidants are difficult to reach, such as fracture layers or clay layers, or when soil or rocks prevent the oxidant from spreading quickly, completely, and evenly. Leaching can leach out DNAPL contaminants present in the soil, and then oxidizing the precipitated DNAPL contaminants with an oxidant can improve the remediation effect. The effectiveness of the oxidant is particularly important. Therefore, a new type of remediation agent is needed to solve the above problems. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a repair agent and its preparation method for repairing DNAPL contamination based on chemical oxidation.

[0005] The technical solution of this invention is: a retrieval agent based on chemical oxidation for repairing DNAPL contamination, comprising 32.5~49.5wt% oxidant and 50.5~67.5wt% composite leaching agent.

[0006] The composite rinsing agent is composed of 12.5~24.5wt% sodium dodecyl sulfate, 21.5~32.9wt% plant polyene polyoxyethylene ether (plant-type polyene phenol NSF), 6~18wt% polyethylene glycol and 24.6~60wt% deionized water.

[0007] In one embodiment of the present invention, the oxidant is selected from any one of potassium permanganate, hydrogen peroxide, or sodium persulfate.

[0008] Note: Oxidants can chemically react with DNAPL contaminants, oxidizing and decomposing them into non-toxic or low-toxic small molecules, or even completely mineralizing them into carbon dioxide and water. This decomposition and transformation process can significantly reduce the toxicity of contaminants and lessen their harm to the environment and human health. By adding the aforementioned oxidants, the degradation process of DNAPL contaminants can be accelerated, improving remediation efficiency. Especially in areas difficult to remediate, such as low-permeability aquifers, contaminants can be removed more effectively, reducing remediation costs and time.

[0009] This invention also provides a method for preparing a remediation agent when the oxidant is any one of potassium permanganate, hydrogen peroxide, or sodium persulfate. Sodium dodecyl sulfate, plant polyene phenol polyoxyethylene ether, and polyethylene glycol are added sequentially to deionized water and mixed to obtain a composite rinsing agent. The oxidant and the composite rinsing agent are stored separately.

[0010] Note: The above method can produce a composite rinsing agent. By storing them separately, the oxidant or the composite rinsing agent can be prevented from being affected. During use, the individual effects of the composite rinsing agent and the oxidant can be maintained to achieve the expected results in the treatment of DNAPL contamination.

[0011] In another embodiment of the present invention, the oxidant is a coated oxidant, which is obtained by coating an oxide core material with stearic acid as the shell material, and the oxide core material is any one of potassium permanganate and sodium persulfate.

[0012] Note: The above-mentioned oxidant design can control the non-selective consumption of the remediation agent, thereby improving the removal efficiency of DNAPL contaminants and solving the problem of poor long-term effectiveness of DNAPL contamination. Furthermore, by using a coated oxidant, it can be pre-mixed with the composite rinsing agent, thereby optimizing the application process of the remediation agent. There is no need to add the composite rinsing agent and oxidant in steps, simplifying the operation process and improving the ease of use of the remediation agent.

[0013] Furthermore, the preparation method of the coated oxidant is as follows:

[0014] 1) Mix stearic acid and cyclohexane at a ratio of 100~200g:1L and stir, while heating in a water bath to 73~78℃. After the stearic acid is completely dissolved, a mixed base solution is obtained.

[0015] 2) Add the oxide core material to the mixed base liquid and ultrasonically stir for 10-20 minutes to make the oxide core material uniformly dispersed in the mixed base liquid. The oxide core material and cyclohexane are added at a ratio of 50-100g:1L.

[0016] 3) Polyethylene glycol is added to the mixed base liquid in batches, while the water bath temperature is reduced to room temperature at a cooling rate of T °C / min to obtain the precipitate, wherein the amount of polyethylene glycol added at one time is M g / min;

[0017] 4) The precipitate was then placed in an oven at 40-50°C for curing for 3-5 hours. During this period, the precipitate was stirred for 3-5 minutes every 20-40 minutes, and a composite liquid accounting for 2-5% of the mass of the precipitate was sprayed on it. Finally, it was crushed and sieved to obtain the coated oxidant.

[0018] Among them, the cooling amplitude of the mixed base liquid The temperature range is 48~53℃, and the cooling rate T ∈ [2, 5], unit: ℃ / min;

[0019] Polyethylene glycol and cyclohexane are added at a ratio of 30-50g:1L, and the total amount of polyethylene glycol added, M0, is 30-50g, where M satisfies the following formula:

[0020]

[0021] Where M is the amount of polyethylene glycol added at one time, in g / min.

[0022] Note: The above method can effectively prepare oxidants with slow-release function. However, the cooling rate and the polyethylene glycol addition rate affect the precipitation rate of stearic acid, which prevents stearic acid from being evenly dispersed around the oxide core material, thus affecting the performance of some coated oxidants. Therefore, by optimizing the polyethylene glycol addition rate and cooling rate, coated oxidants with better performance can be obtained.

[0023] Meanwhile, by applying the composite liquid at regular intervals and in quantitative amounts during the solidification of the precipitate, and by using the composite liquid in conjunction with temperature variations, the structure of the coated oxidant is strengthened, which can further improve the effectiveness of the coated oxidant and thus enhance the effectiveness of the remediation agent in the treatment of DNAPL contamination.

[0024] Furthermore, since the cooling rate and the polyethylene glycol addition rate affect the precipitation rate of stearic acid, the above formula provides guidance for the single addition amount of polyethylene glycol. This method enables stearic acid to be uniformly dispersed around the oxide core material, thereby improving the performance of the coated oxidant and obtaining a coated oxidant with superior performance.

[0025] Furthermore, the composite solution comprises 2-7 wt% carboxypropyl methylcellulose, 5-18 wt% acetic acid, and 75-93 wt% deionized water, and the temperature of the composite solution is 17-20°C.

[0026] Note: By adding carboxypropyl methylcellulose and acetic acid to deionized water in a certain proportion, and combining this with low temperature during the curing process of the coated oxidant, the effectiveness of the prepared coated oxidant can be significantly improved, thereby enhancing the remediation effect of the repair agent on DNAPL contamination.

[0027] This invention also provides a method for preparing a coating-type oxidant, wherein the coating-type oxidant is a repair agent used when stearic acid is used as the shell material to coat an oxidized core material, comprising the following steps:

[0028] S1. Add sodium dodecyl sulfate, plant polyene polyoxyethylene ether, and polyethylene glycol to deionized water in sequence and mix well to obtain a composite rinsing agent for later use.

[0029] S2. Mix the coated oxidant and the composite eluent in a ratio of 32.5~49.5wt% and 50.5~67.5wt% respectively to obtain a repair agent for repairing DNAPL contamination.

[0030] Note: The above method can obtain a mixed repair agent. By premixing the coated oxidant and the composite rinsing agent, the application process of the repair agent is optimized. There is no need to add the composite rinsing agent and oxidant in steps, which simplifies the operation process and improves the ease of use of the repair agent.

[0031] Furthermore, the repair agent is prepared and used immediately, and the coated oxidant and the composite rinsing agent are used within 48 hours after being combined.

[0032] Note: To avoid prolonged immersion of the coated oxidant in the composite rinsing agent, the above method can effectively prevent this problem, avoid affecting the slow-release effect of the coated oxidant, and thus ensure the effectiveness of the repair agent.

[0033] The beneficial effects of this invention are:

[0034] (1) The remediation agent of the present invention leaches out DNAPL pollutants present in the soil through the composite leaching agent, and then uses the oxidant to oxidize the precipitated DNAPL pollutants. This solves the problem in the prior art that when DNAPL pollutants are in areas that are difficult for oxidants to reach, such as fracture layers or clay layers, or when soil or rocks prevent the oxidant from spreading quickly, completely and evenly, the remediation cycle of in-situ chemical oxidation technology will be greatly extended.

[0035] (2) By using a coated oxidant, the present invention can effectively simplify the application steps of the repair agent, without the need to add the composite rinsing agent and oxidant in steps, and the oxidizing activity is long-lasting, which can effectively control the release of the oxidized core material, reduce the non-selective consumption of the oxidant, and improve the removal efficiency of DNAPL pollutants.

[0036] (3) By optimizing the preparation method of the coated oxidant, the present invention can improve the performance of the coated oxidant, solve the problem that stearic acid cannot be evenly dispersed around the oxide core material and affect the performance of some coated oxidants, and thus prepare a coated oxidant with better performance. Detailed Implementation

[0037] The present invention will now be described in more detail with reference to specific embodiments, so as to better demonstrate the advantages of the present invention.

[0038] Example 1: A retrieval agent based on chemical oxidation for DNAPL contamination, comprising 45.5 wt% oxidant and 54.5 wt% composite leaching agent. It should be noted that the dosage of the composite leaching agent is adjusted according to the degree of DNAPL contamination.

[0039] The composite rinsing agent is composed of 18.7 wt% sodium dodecyl sulfate, 27.6 wt% plant polyene polyoxyethylene ether (plant-type polyene phenol NSF), 14.5 wt% polyethylene glycol, and 39.2 wt% deionized water. The oxidant is selected from commercially available potassium permanganate.

[0040] The preparation method of the above-mentioned remediation agent is as follows: sodium dodecyl sulfate, plant polyene polyoxyethylene ether, and polyethylene glycol are added to deionized water in sequence and mixed to obtain a composite leaching agent. The oxidant and the composite leaching agent are stored separately. During the treatment of DNAPL pollution, the DNAPL pollutants present in the soil are leached out by the leaching agent, and then the oxidant is used to oxidize the precipitated DNAPL pollutants.

[0041] Example 2: This example differs from Example 1 in that the repair agent includes 32.5 wt% oxidant and 67.5 wt% composite rinsing agent.

[0042] Example 3: This example differs from Example 1 in that the repair agent includes 49.5 wt% oxidant and 50.5 wt% composite rinsing agent.

[0043] Example 4: The difference between this example and Example 1 is that the composite rinsing agent is composed of 12.5 wt% sodium dodecyl sulfate, 21.5 wt% plant polyene polyoxyethylene ether (plant-type polyene phenol NSF), 6 wt% polyethylene glycol and 60 wt% deionized water.

[0044] Example 5: This example differs from Example 1 in that the composite rinsing agent is composed of 24.5 wt% sodium dodecyl sulfate, 32.9 wt% plant polyene polyoxyethylene ether (plant-type polyene phenol NSF), 18 wt% polyethylene glycol and 24.6 wt% deionized water.

[0045] Experiments were conducted to simulate DNAPL contamination, with multiple 3m groups set up. 2 The DNAPL contaminated areas were identified, and the DNAPL content in each contaminated area was kept relatively consistent by DNAPL injection. Subsequently, the DNAPL contaminated areas were treated for 90 days using the same method. The DNAPL removal rate was calculated by comparing the DNAPL contaminated areas before and after 90 days of treatment. The results are shown in Table 1 below.

[0046] Table 1. DNAPL removal rate in DNAPL-contaminated areas after 90 days of remediation.

[0047]

[0048] Meanwhile, a control group treated with only oxidant was set up to compare the DNAPL contamination areas before and after 90 days of remedy, and the DNAPL removal rate was calculated. The results are shown in Table 2 below:

[0049] Table 2. DNAPL removal rate in DNAPL-contaminated areas after 90 days of remediation.

[0050]

[0051] As shown in Tables 1 and 2 above, the DNAPL removal rate was significantly better than the control when using the combined rinsing agent and oxidant. Furthermore, there were some differences in the treatment of DNAPL-contaminated areas when using different doses of oxidant and combined rinsing agent, as detailed below:

[0052] 1) In Example 2, the DNAPL removal rate decreased after reducing the amount of oxidant and increasing the amount of composite rinsing agent. This may be because even with sufficient rinsing, the insufficient amount of oxidant affected the removal effect of DNAPL. In Example 3, the DNAPL removal rate also decreased after increasing the amount of oxidant and reducing the amount of composite rinsing agent. This may be because the rinsing was insufficient, and the DNAPL contaminants were located in areas that the oxidant could not easily reach, such as fracture layers or clay layers. Alternatively, the soil or rocks prevented the oxidant from spreading quickly, completely, and evenly. Therefore, even if the amount of oxidant was too high, the DNAPL removal rate could not be improved.

[0053] 2) For Examples 4 and 5, the DNAPL removal rate decreased after the composition of the composite rinsing agent was changed. It can be seen that the composite rinsing agent of Example 1 has the best effect in rinsing and the best rinsing effect.

[0054] Example 6: The difference between this example and Example 1 is that the oxidant is commercially available hydrogen peroxide.

[0055] Example 7: The difference between this example and Example 1 is that the oxidant is commercially available sodium persulfate.

[0056] Example 8: This example differs from Example 1 in that the oxidant is a coated oxidant, obtained by coating an oxide core material with stearic acid as the shell material. The oxide core material is potassium permanganate. The preparation method of the coated oxidant is as follows:

[0057] 1) Mix stearic acid and cyclohexane at a ratio of 160g:1L and stir, while heating in a water bath to 76°C. After the stearic acid is completely dissolved, a mixed base solution is obtained.

[0058] 2) Add the oxide core material to the mixed base liquid and ultrasonically stir for 15 minutes at a stirring speed of 300 r / min to make the oxide core material uniformly dispersed in the mixed base liquid. The oxide core material and cyclohexane are added in a ratio of 80 g: 1 L.

[0059] 3) Polyethylene glycol is added to the mixed base liquid in batches, while the water bath temperature is reduced to room temperature (25°C) at a cooling rate of T°C / min to obtain the precipitate, wherein the amount of polyethylene glycol added at one time is M g / min;

[0060] 4) The precipitate was then placed in a 45°C oven for curing for 4 hours. During this period, the precipitate was stirred for 4 minutes every 30 minutes at a stirring speed of 150 r / min. A composite liquid accounting for 4.5% of the mass of the precipitate was also sprayed on it. Finally, the precipitate was crushed and sieved to obtain the coated oxidant.

[0061] The composite solution comprises 5 wt% carboxypropyl methylcellulose, 16 wt% acetic acid, and 79 wt% deionized water, and the temperature of the composite solution is 18°C.

[0062] Temperature drop of mixed base liquid The temperature is 51℃, and the cooling rate T ∈ 4℃ / min;

[0063] Polyethylene glycol and cyclohexane are added at a ratio of 40g:1L, and the total amount of polyethylene glycol added, M0, is 40g. M satisfies the following formula:

[0064]

[0065] Where M is the amount of polyethylene glycol added at one time, in g / min;

[0066] The calculated value of M is 3.14 g / min. It should be noted that the rounding is performed using a place value system.

[0067] The preparation method of the above-mentioned repair agent includes the following steps:

[0068] S1. Add sodium dodecyl sulfate, plant polyene polyoxyethylene ether, and polyethylene glycol to deionized water in sequence and mix well to obtain a composite rinsing agent for later use.

[0069] S2. The coated oxidant and the composite eluent are mixed in a ratio of 45.5 wt% oxidant and 54.5 wt% composite eluent to obtain a repair agent for repairing DNAPL contamination.

[0070] It should be noted that the repair agent is prepared and used immediately, and the coating oxidant and the composite rinsing agent are used within 48 hours after being mixed. The repair agent of the present invention can be used directly as a liquid repair agent by means of spraying, burying, stirring, etc.

[0071] Example 9: This example differs from Example 8 in that stearic acid and cyclohexane are mixed and stirred at a ratio of 100g:1L, the oxidized core material is added at a ratio of 100g:1L, and polyethylene glycol is added at a ratio of 50g:1L.

[0072] Example 10: This example differs from Example 8 in that stearic acid and cyclohexane are mixed and stirred at a ratio of 200g:1L, the oxidized core material is added at a ratio of 50g:1L, and the polyethylene glycol is added at a ratio of 30g:1L.

[0073] Example 11: The difference between this example and Example 8 is that the water bath is heated to 73°C.

[0074] Example 12: The difference between this example and Example 8 is that the water bath is heated to 78°C.

[0075] Example 13: The difference between this example and Example 8 is that the oxide core material is added to the mixed base liquid and ultrasonically stirred for 10 minutes at a stirring speed of 200 r / min.

[0076] Example 14: The difference between this example and Example 8 is that the oxide core material is added to the mixed base liquid and ultrasonically stirred for 20 minutes at a stirring speed of 400 r / min.

[0077] Example 15: This example differs from Example 8 in that polyethylene glycol is added to the mixed base solution sequentially, with a single addition amount of M g / min, and the water bath temperature is reduced to room temperature at a cooling rate of 2 °C / min, where M satisfies the following formula:

[0078]

[0079] Where M is the amount of polyethylene glycol added at one time, in g / min;

[0080] The calculated value of M is 1.57 g / min.

[0081] Example 16: This example differs from Example 8 in that polyethylene glycol is added to the mixed base solution sequentially, with a single addition amount of M g / min, and the water bath temperature is reduced to room temperature at a cooling rate of 5 °C / min, where M satisfies the following formula:

[0082]

[0083] Where M is the amount of polyethylene glycol added at one time, in g / min;

[0084] The calculated value of M is 3.93 g / min.

[0085] Example 17: The difference between this example and Example 8 is that the precipitate is placed in a 40°C oven for curing for 5 hours. During this period, the precipitate is stirred for 3 minutes every 20 minutes, and a composite liquid accounting for 5% of the mass of the precipitate is sprayed on it.

[0086] Example 18: The difference between this example and Example 8 is that the precipitate is placed in a 50°C oven for curing for 3 hours. During this period, the precipitate is stirred for 5 minutes every 40 minutes, and a composite liquid accounting for 2% of the mass of the precipitate is sprayed on it.

[0087] Example 19: This example differs from Example 8 in that the composite liquid includes 2 wt% carboxypropyl methylcellulose, 5 wt% acetic acid and 93 wt% deionized water, and the temperature of the composite liquid is 17°C.

[0088] Example 20: This example differs from Example 8 in that the composite liquid includes 7 wt% carboxypropyl methylcellulose, 18 wt% acetic acid and 75 wt% deionized water, and the temperature of the composite liquid is 20°C.

[0089] To further verify the effectiveness of each remediation agent, the above-described method was used to treat DNAPL-contaminated areas for 90 days using the remediation agents from each embodiment. The DNAPL-contaminated areas before and after 90 days of remediation were compared, and the DNAPL removal rate was calculated. The results are shown in Table 3 below:

[0090] Table 3. DNAPL removal rate in DNAPL-contaminated areas after 90 days of remediation.

[0091]

[0092] As shown in Table 3 above, the DNAPL removal rate of the remediation method using the combined rinsing agent and the coated oxidant was significantly better than that of Example 1. However, there were some differences in the treatment of DNAPL contaminated areas when using the coated oxidant and the combined rinsing agent, which are analyzed in detail below:

[0093] 1) In Example 9, after increasing the proportion of the oxidized core material relative to stearic acid, the DNAPL removal rate decreased. This may be because the oxidized core material was not completely surrounded by stearic acid, thus affecting the sustained-release performance of the prepared product. Similarly, in Example 10, after reducing the proportion of the oxidized core material relative to stearic acid, the DNAPL removal rate also decreased. This may be because the proportion of the oxidized core material in the coated oxidant was too small, which indirectly affected the amount and effect of the oxidant. Therefore, the ratio of oxidized core material to stearic acid in Example 8 is relatively optimal and has a better effect in actual DNAPL pollution control.

[0094] 2) Regarding Examples 11 and 12, after changing the water bath temperature, the DNAPL removal rate of Example 11 decreased to a certain extent, while Example 12 was basically the same as Example 8. This may be because the low temperature affected the dispersion and dissolution effect of the mixed system. Example 12 requires more heat energy to reach that temperature value. Therefore, the overall effect of Example 8 is relatively better.

[0095] 3) For Examples 13 and 14, after changing the ultrasonic stirring time and stirring speed, the DNAPL removal rate of Example 13 decreased to a certain extent, while Example 14 was basically the same as Example 8. This may be because the mixed system was already evenly dispersed under the ultrasonic stirring parameters of Example 8, and further increasing the ultrasonic stirring time and stirring speed could not further enhance the dispersion. At the same time, Example 14 required more energy to achieve the parameters. Therefore, the overall effect of Example 8 was relatively better.

[0096] 4) For Examples 15 and 16, after calculating the M value using the formula of the present invention, a relatively stable coating effect of the oxidant can be achieved according to different cooling rates. Examples 15 and 16 have slight differences compared to Example 8, but Example 15 takes longer overall, while Example 16 takes shorter overall. Therefore, the appropriate choice can be made according to the actual production situation.

[0097] 5) For Examples 17 and 18, the DNAPL removal rate decreased to some extent after the parameters of the solidification treatment were changed. This may be because in Example 17, too much composite liquid was used, which affected the solidification effect of the precipitate and thus the slow-release performance of the coated oxidant. On the other hand, too little composite liquid was used, which affected the effect of the composite liquid and thus the performance of the coated oxidant. Therefore, the solidification treatment parameters and the use of composite liquid in Example 8 are relatively optimal and have a better effect in actual DNAPL pollution control.

[0098] 6) For Examples 19 and 20, the DNAPL removal rate decreased after the composition of the composite solution was changed. It can be seen that the composite solution of Example 8 has the best effect in the curing process.

[0099] Meanwhile, to further verify the effectiveness of the composite solution, three composite solutions were prepared: one using only carboxypropyl methylcellulose and deionized water (to make up the difference) (Control 1); one using only acetic acid and deionized water (to make up the difference) (Control 2); and one prepared with the same composition as in Example 8 but at the same temperature (Control 3). The DNAPL contaminated areas before and after 90 days of remediation were compared, and the DNAPL removal rate was calculated. The results are shown in Table 2 below.

[0100] Table 4. DNAPL removal rate in DNAPL-contaminated areas after 90 days of remediation.

[0101]

[0102] As shown in Table 4 above, the DNAPL removal rate decreased to some extent after using different composite solutions. This indicates that the composite solution composed of carboxypropyl methylcellulose and acetic acid added to deionized water in a certain proportion can enhance the material properties of the coated oxidant, thereby improving the treatment effect of the remediation agent in DNAPL. However, the effectiveness of the prepared coated oxidant also decreased significantly after eliminating the temperature difference between the composite solution and the precipitate. Therefore, by rationally combining the composite solution and coordinating with temperature difference changes, the effectiveness of the coated oxidant can be further improved, thereby enhancing the effectiveness of the remediation agent in the treatment of DNAPL pollution.

Claims

1. A remediation agent based on chemical oxidation for repairing DNAPL contamination, characterized in that, It includes 32.5~49.5wt% oxidant and 50.5~67.5wt% composite rinsing agent. The composite rinsing agent is composed of 12.5~24.5wt% sodium dodecyl sulfate, 21.5~32.9wt% plant polyene polyoxyethylene ether, 6~18wt% polyethylene glycol and 24.6~60wt% deionized water; The oxidant is a coated oxidant, which is obtained by coating an oxide core material with stearic acid as the shell material. The oxide core material is either potassium permanganate or sodium persulfate. The preparation method of the coated oxidant is as follows: 1) Mix stearic acid and cyclohexane at a ratio of 100~200g:1L and stir, while heating in a water bath to 73~78℃. After the stearic acid is completely dissolved, a mixed base solution is obtained. 2) Add the oxide core material to the mixed base liquid and ultrasonically stir for 10-20 minutes to make the oxide core material uniformly dispersed in the mixed base liquid. The oxide core material and cyclohexane are added at a ratio of 50-100g:1L. 3) Polyethylene glycol is added to the mixed base liquid in batches, while the water bath temperature is reduced to room temperature at a cooling rate of T °C / min to obtain the precipitate, wherein the amount of polyethylene glycol added at one time is M g / min; 4) The precipitate was then placed in an oven at 40-50°C for curing for 3-5 hours. During this period, the precipitate was stirred for 3-5 minutes every 20-40 minutes, and a composite liquid accounting for 2-5% of the mass of the precipitate was sprayed on it. Finally, it was crushed and sieved to obtain the coated oxidant. Among them, the cooling amplitude of the mixed base liquid The temperature range is 48~53℃, and the cooling rate T ∈ [2, 5], unit: ℃ / min; Polyethylene glycol and cyclohexane are added at a ratio of 30-50g:1L, and the total amount of polyethylene glycol added, M0, is 30-50g, where M satisfies the following formula: Where M is the amount of polyethylene glycol added at one time, in g / min; The composite solution comprises 2-7 wt% carboxypropyl methylcellulose, 5-18 wt% acetic acid, and 75-93 wt% deionized water, and the temperature of the composite solution is 17-20°C. The preparation method of the above-mentioned retrieval agent based on chemical oxidation for DNAPL contamination includes the following steps: S1. Add sodium dodecyl sulfate, plant polyene polyoxyethylene ether, and polyethylene glycol to deionized water in sequence and mix well to obtain a composite rinsing agent for later use. S2. Mix the coated oxidant and the composite eluent in a ratio of 32.5~49.5wt% and 50.5~67.5wt% respectively to obtain a repair agent for repairing DNAPL contamination.

2. The retrieval agent for DNAPL contamination based on chemical oxidation as described in claim 1, characterized in that, The repair agent is prepared and used immediately. The core material of the coating oxidant is either potassium permanganate or sodium persulfate. The coating oxidant and the composite rinsing agent are used within 48 hours after being mixed.

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